Neptune

December 28, 1612: Galileo Galilei observes the planet Neptune. In his drawings of the night sky, Neptune is placed appropriately but mislabeled as a fixed star. Because of this, Galileo is not credited with the discovery of the planet. A fixed star is a celestial object that does not seem to move in relation to other stars. The ancients saw two groups of objects in the night sky. Fixed stars all seemed to span the night sky in unison while the wandering stars moved independently. Fixed stars are really stars while wandering stars are the naked eye visible planets. A second difference between the two is that stars twinkle while planets shine.

Galileo again drew Neptune in the same place on January 27, 1613. Because the planet is so distant and its orbital path so large, the planet had not seemed to shift. It was thought to be a star. The planet was discovered after it was theoretically proven to exist. Gravitational disturbances in the orbit of Uranus led to conjecture of another more distant planet. Urbain Le Verrier mathematically figured out where this disturbance was coming from. Johann Gottfried Galle viewed the math projection and so pointed his telescope to the appropriate portion of the sky. Others were also working on the math and looking at the sky; priority was in dispute.

Neptune is the eighth and now last planet from the sun. It appears blue because red light is absorbed by methane. The planet’s mass is 17 times that of Earth but just 1/19th that of Jupiter. Neptune is the smallest of the gas giants. Since both Uranus and Neptune have a much higher concentration of volatiles (elements or compounds with low boiling points) when compared to Jupiter and Saturn, they are sometimes referred to as ice giants instead of gas giants. The planet sports a ring system although far less impressive than Saturn’s.

Neptune’s average distance from the Sun is 30.1 AU or 30.1 times farther than Earth’s orbit from the Sun. It takes 164.79 years for Neptune to orbit the Sun. On July 12, 2011, it will be 1 Neptune year since it was discovered in 1846. Neptune has 13 known moons, but most are so small they were not massive enough to achieve a spherical shape. The largest moon, Triton, contains 99% of the lunar mass and was found just 17 days after Neptune was discovered. Voyager 2 passed the planet in 1989, sending back information about the planet and moons.

“The exploration of the solar system cannot be what we want it to be as an enterprise borne solely by the American taxpayer or indeed even by the taxpayers of the nations willing to join with us in this enterprise.” – Michael Griffin

“The science data set to return next year will have a huge impact on the way in which we deal with conditions on Earth, demonstrating how the exploration of the solar system has real impact on our daily lives.” – Keith Mason

“Four and a half billion years ago, all of the matter of the solar system, including us, was part of a giant molecular cloud. Genesis is providing the chemical composition of that solar nebula. …The material is still stored for us in the surface of the sun.” – Don Burnett

“We’ll learn more about the relationship between the rings and satellites…and a lot of the models that will be tested also apply to galactic formation and the origin of our solar system.” – Bonnie Buratti

This article first appeared at examiner.com in 2009. Editor’s update: Urbain Le Verrier was a French mathematician who is one of the people credited with discovering Neptune. By observing Uranus and doing complicated calculations, he was able to posit a planet’s existence farther out. Le Verrier announced his finding publicly to the French Academy two days before Englishman John Couch Adams mailed a final solution to the Royal Greenwich Observatory. Le Verrier mailed his finding to Johann Galle at the Berlin Observatory and the letter arrived on September 23, 1846. That night, Galle and Heinrich d’Arrest found the planet just 1° from where Le Verrier had predicted. Adams himself acknowledged Le Verrier’s priority.

Also on this day: Child’s Play – In 1973, Akron, Ohio stops their association with Box Car Derby after cheating becomes rampant.Poor Ben – In 1732, an ad for Poor Richard’s Almanack was run in Ben Franklin’s newspaper.San Francisco Muni – In 1912, the Municipal Railroad in San Francisco opened.